In semiconductor devices for use in computers, miniaturization of wiring widths, referred to as design rules, has advanced year by year in order to realize further higher integration and higher speed. Therefore, there are an increased number of cases where nanometer-scaled substrate surface defects, which had not been conventionally problematic, have adverse effects on performances of semiconductor devices. Accordingly, it is highly important to deal with nanometer-scaled substrate surface defects.
For polishing a silicon substrate among semiconductor substrates, a polishing composition containing silica particles and a water-soluble polymer is suitably used (see, for example, Patent Document 1). The polishing composition disclosed in Patent Document 1 forms a protective film derived from the water-soluble polymer on the surface of a polished silicon substrate. This protective film imparts hydrophilicity to the surface of the polished substrate, thereby making easier handling of the polished substrate. However, the water-soluble polymer used for the polishing composition has a molecular weight of several hundred thousands or more, and thus forms aggregates together with the silica particles. The aggregates made of the silica particles and the water-soluble polymer may cause substrate surface defects, which are referred to as light point defects (LPDs).
In order to reduce LPDs due to aggregates made of silica particles and water-soluble polymer, it is important to eliminate aggregates from the polishing composition. As one example therefor, it is effective that when polishing composition containing silica particles and water-soluble polymer is produced and used, the polishing composition be subjected to filtration by a filter to remove aggregates. However, the polishing composition immediately causes clogging of the filter, and thus there is a problem that the filter must be frequently exchanged.
In order to improve the dispersibility of abrasive grains in a polishing composition, compounding of a dispersant or the like in the polishing composition has been proposed. Patent Document 2 discloses that a surfactant is added to a polishing composition to thereby improve the dispersibility of abrasive grains. However, the polishing composition disclosed in Patent Document 2 includes no water-soluble polymer that has a molecular weight of several hundred thousands or more and is predicted to form aggregates together with abrasive grains. Patent Document 2 only discloses that the polishing composition to which the surfactant is added is used to thereby improve the polishing rate of a wafer.
Patent Document 3 discloses a water-based dispersion for polishing, containing a water-soluble polymer, and a surfactant as dispersants. However, the water-based dispersion for polishing includes no water-soluble polymer having a molecular weight of several hundred thousands or more, the polymer being predicted to form aggregates together with abrasive grains. Patent Document 3 only discloses that the water-based dispersion for polishing, to which the dispersants are added, is used to thereby reduce scratches on a copper film.
Furthermore, Patent Document 4 discloses a polishing composition containing at least one water-soluble polymer selected from polyvinylpyrrolidone and poly(N-vinylformamide), and an alkali. It also discloses that the polishing composition is effective for reducing LPDs. However, Patent Document 4 discloses no polishing composition including a water-soluble polymer having a molecular weight of several hundred thousands or more, the polymer being predicted to form aggregates together with abrasive grains, and it does not disclose the dispersibility of abrasive grains.
Accordingly, there is a need for a polishing composition that imparts high hydrophilicity to the surface of a polished substrate, reduces LPDs, and achieves a high dispersibility of abrasive grains.